In the twilight of an overcast mid-August dusk, members of the Hartland Nature Club in Hartland, Vermont, gathered by the side of a trim white farmhouse. At 7:28 pm, a small, dark animal dropped from the roof and sped off overhead. Shortly thereafter, groups of four, then two, a pause, then three more animals emerged from under the slate shingles of the traditional Vermont house and sped off to break their fast at a nearby pond.
Nine species of bats live in New Hampshire and Vermont, though only a few utilize human-built structures for day roosts. Chiroptera, the “hand-winged animals,” are one of the most diverse groups of mammals, second only to rodents. Unlike rodents, however, and more like their distant avian cousins, the swallows, most bats are migratory.
Dr. Thomas Kunz of Boston University notes that our three tree bat species, the red bat (Lasiurus borealis), the hoary bat (Lasiurus cinereus), and the silver-haired bat (Lasionycteris noctivagans), move south in late summer and early autumn before hibernating. These bats are among our larger species, with wing spans of 12 inches or more. The remarkable hoary bat has a wing span of 16 inches, flies at speeds up to 60 mph, and ranges as far north as Hudson Bay during the summer.
The big brown bat (Eptesicus fuscus) is the second largest bat in our area, with a wingspan of up to 12.9 inches and a weight of .56 ounces (the equivalent of three quarters). Big brown bats are the most familiar bats, since they often roost around houses, and maternal colonies (where female bats congregate in the spring and summer to raise their pups) are often formed in buildings. The big brown usually stays close to the same site, both summer and winter, though some individuals have been tracked returning to roosts from as far as 450 miles away.
Five bats – the little brown bat (Myotis lucifugus), the northern long-eared bat (Myotis septentrionalis), the eastern small-footed bat (Myotis leibii), the eastern pipistrelle (Pipistrellus subflavus), and the Indiana bat (Myotis sodalis) – migrate west and sometimes north to seek the rare sites needed for successful hibernation. As bats migrate, they are feeding and gathering fat reserves for a long period of starvation. Within a suitable cave or mine, each species of bat locates in a slightly different area, all seeking a narrow range of temperature, humidity, air circulation, and micro-topography. Many of the little brown bats in the twin states migrate west to a cave on Mount Aeolus in Dorset, Vermont. A banding study by Wayne Davis and Harold Hitchcock revealed that this hibernaculum is used by little brown bats from as far away as Rhode Island.
Dr. Scott Reynolds, of Concord, New Hampshire, notes that the Connecticut Valley has a healthy bat population but that not many specific colonies have been identified. A large maternal colony of bats used to live in the attic of an old brick building in Cornish, New Hampshire, before the site was disrupted. Bats visited this colony well into September, long after most maternal colonies have typically dispersed, and John Kantor, of the New Hampshire Fish and Game Department, hypothesized that the site was also functioning as a stopover site for bats migrating west to Mount Aeolus in Vermont.
While dangers to bats include predation, disturbance during hibernation, and pesticides, one of the most critical injuries comes from habitat destruction. For bats, the critical elements of habitat are food sources, hibernacula, and daily roosting sites.
By the end of August, the cave on Mount Aeolus is locked with iron bars to prevent human disturbance during the winter. In the state’s Wildlife Action Plan, the Vermont Fish and Wildlife Department prioritizes a need to collaborate with landowners such as The Nature Conservancy (owners of the cave) and recreation groups such as the Vermont Cavers Association to protect bat hibernacula. The distribution of maternal colonies and stopover sites is much less well known and understood.
Back at the Hartland farmhouse, the last of the small bats had emerged shortly after 8 P.M. and flown off. No one knows how long the bats have been coming here to raise their pups in this maternal colony. Perhaps they arrived when the house was new and the landscape was bereft of old shade trees. For now, the bats are safe and enjoyed by the human residents of the house, and the emergence and flight of the bats was duly celebrated by the community.
By the end of the evening, we had counted 128 bats emerging from the roost. A couple of individuals, probably males, had spent the day behind a shutter, finally emerging after dark to fly a couple of loops on the porch with stunning precision before disappearing.
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